The present invention relates to anesthesia, especially local anesthetics. More particularly, this invention relates to a method for controlling the duration of local anesthesia, and to a reagent system or kit for inducing and limiting or reversing local anesthesia produced.
Anesthetic agents are pharmacologically active agents that block nerve conduction when applied in therapeutically effective amounts. They can be used for local application, namely to a localized area, for example, by application to the skin or other dermal membrane, or for systemic application, e.g., by the intraperitoneal or intravenous routes of administration.
The anesthetic agent may be applied locally by injection, ointments, jellies, topical solutions and suspensions or other forms known for topical administration.
Local anesthetics generally are esters or amides of benzoic acid, typically administered as an acid addition salt in dosages known to those skilled in the art.
For example, as applied to the region of the mouth and adjacent areas of humans, anesthesia involves injection of anesthetic agents including roughly 2 to 3% lidocaine, 2 to 3% mepivacaine, 0.5% marcaine or 3 to 4% prilocaine, usually administered in aqueous solution in the form of a water-soluble acid-addition salt, typically the hydrochloride salt. Also, as practiced, vasoconstricting agents such as epinephrine, phenylphrine or levonordenphedrine may be administered concomitantly or separately with the local anesthetic agent in order to prolong the duration of the local anesthesia, reportedly by constriction of blood vessels, resulting in prolongation of the contact of the anesthetic with the nerve.
Aqueous Lidocaine hydrochloride in sodium bicarbonate has been used in spinal and epidural anesthesia to speed up the onset of anesthesia to reduce the burning upon injection and to lengthen the duration of action.
In some areas, especially in the mouth, the local anesthesia may last longer than needed. This is debilitating and restrictive to the patient's normal activity. The administration of a local anesthetic at relatively low pH, typically in the range of about pH 2 to about pH 5.5, has been reported to retard the duration of anesthetic action.